a) Field of the Invention
The invention is directed to a tribo-system with a first structural component part and a second structural component part, wherein these structural component parts are in dry frictional contact with one another, each through a surface layer, and to a process for the manufacture of a tribo-system of this type.
b) Description of the Related Art
The invention relates in particular to the material construction of tribo-systems (friction systems) in the aviation and aerospace industry that operate without liquid lubricants or lubricating grease and whose structural component parts are loaded by temperatures of up to 2000.degree. C., for example, in reusable launchers, hypersonic airborne vehicles and hypersonic aircraft, reentry airborne vehicles and in high-temperature components or components in the hot part of propulsion units such as, e.g., aircraft engines.
All known liquid lubricants are thermally unstable in air above a continuous sump temperature of 200.degree. C. and at temporary temperature peaks above 350.degree. C. and pass into the gaseous phase at temperatures above 400.degree. C., so that they are scarcely usable except as disposable lubricants, although this is to be avoided for ecological-toxicological reasons.
Efforts continue to be made to provide friction locations with lubricants through a gaseous surrounding medium, wherein the lubricants form lubricating connections with the friction surfaces only upon frictional contact by decomposition or reaction with these friction surfaces. However, substances such as tricresyl phosphate, phthalocyanine or aryl phosphate which are mixed in with the gas require other operating means with regulating and controlling technology on the one hand and, on the other hand, are also objectionable in ecological and toxicological respects to the same extent as the previously known substances.
In the case of high-temperature applications in tribo-systems above 400.degree. C., there has been no shortage of attempts in the past to ensure reliable tribological operation over the long term, for example, by arranging solid lubricants in layers and material matrices or by coating directly with solid lubricants. These attempts did not prove successful in practice, however, because all of the known intrinsic solid lubricants lose their favorable tribological properties as the surrounding temperature increases and/or as the oxygen partial pressure increases. Further, solid lubricants which are arranged in material matrices are considerably weakened with respect to their mechanical characteristics and coating capability.
Therefore, tribo-systems used in the aviation and aerospace industry which are subjected to structural component temperatures of 700.degree. C. to 2000.degree. C. through the heat conduction of friction heat and process heat in the friction locations and which therefore chiefly run dry are generally either discarded as unrealizable or are installed in cooler regions following suitable heat sinks and with appropriate thermal insulation. In the latter case, the resulting constructions are bulky and accordingly take up excessive space and are also heavy and therefore uneconomical in terms of weight. Nevertheless, such embodiment forms can usually only be used once for a flight mission and are serviced and repaired after every use.
The tribological behavior of the materials chiefly used at the present time for the material construction of tribo-systems during dry running limits the life of the products and systems outfitted with the tribo-system because the extent of wear or wear coefficient of the pairing of materials is too high at &gt;10.sup.-5 mm.sup.3 /Nm. Consequently, determined constructions with long wear distance and large allowed tolerances must be used so that the friction locations do not undergo adhesive failure, i.e., so that they do not fuse (or "seize"). Such measures against adhesive failure always increase the wear coefficient with increasing temperature or, in other words, increase wear and allow only a short useful life. Other failure criteria determining the life of these products are material degradation, especially due to oxidation, phase transition, and creep.
Bearing materials of Cr.sub.3 C.sub.2 -CaF.sub.2 which have wear coefficients greater than 5.times.10.sup.-5 mm.sup.3 /Nm at 700.degree. C. have been suggested, for example, for the friction locations operating at approximately 700.degree. C. in the HERMES space shuttle. CaF.sub.2, as extrinsic solid lubricant, softens at approximately 1000.degree. C. and also separates due to the high wear coefficient when applied as bearing material at temperatures up to 2000.degree. C.